High-voltage transformer



Dec. 17, 1946. A. G. GANZ 2,412,609

HIGH VOLTAGE TRANSFORMER Filed Jan. 15, 1944 FIG.

76. 2 FIG. a FIG; 4

muszmummj mumwf inumumm FIGS INVENTOR A. ,6- GANZ A TTORNEY PatentedDec. 17, 1946 UNITED STATES PATENT OFFICE HIGH-VOLTAGE TRANSFORMERAlbert G. Ganz, New York, N. Y., assignor to Bell TelephoneLaboratories, Incorporated, New York, N. Y., a corporation of New YorkApplication January 15, 1944, Serial No. 518,363

7 Claims. 1

This invention relates to transformers and particularly to transformerssubjected to high voltages.

In high voltage transformers the insulation between windings is ofconsiderable importance in insuring against transformer failure inservice. Increasing th amount of insulation between the windings is oneway of obtaining a high safety factor, but increasing the insulationincreases transformer size and cost and reduces the transformerefficiency, particularly where a wide band of frequencies istransmitted. Where space is limited and weight must be a minimum, as forexample in airplanes, means for increasing the effectiveness ofinsulation is especially valuable since it reduces the amount that wouldbe required.

An object of the present invention is a high voltage transformer inwhich the thickness of insulation between windings is reduced whilestill retaining a high safety factor.

Another object of the invention is a high voltage transformer having ahigh efficiency and which is of small size and low weight in relation tothe voltage and power involved.

A further object of the invention is to increase the uniformity of thepotential gradient across the insulation between the windings of a highvoltage transformer.

In one embodiment, this invention comprises a single layer auxiliarywinding between a single layer secondary winding and a single layerprimary winding of the transformer. This auxiliary winding isopen-circuited. When the primary winding is subjected to a voltage,there is induced in the auxiliary winding a voltage dependent upon thenumber of turns of the auxiliary winding. If the auxiliary winding islocated between the secondary winding and the primary winding at aproper position determined by the number of turns therein, theinsulation is effectively divided into two sections, each of which issubjected to only a fraction'of the original voltage. The potentialgradients throughout the insulation will, therefore, be maintained morenearly uniform.

Th invention will be better understood from the following description inconnection with the attached drawing, in which:

Fig. 1 is a partial section of a simplified form of transformerembodying the invention;

Fig. 2 is a schematic circuit of the transformer of Fig. 1;

Fig. 3 is a schematic circuit of a transformer in which two auxiliarywindings are used;

Fig. 4 is a schematic circuit of a transformer showing the arrangementwhen a grounded shield and one auxiliary winding are used; and

Fig. 5 is a schematic circuit of a transformer showing the arrangementwhen a grounded shield and two auxiliary windings are used like parts inthe different figures having like indicia.

The simplified form of th invention shown in Fig. 1 shows a part of thecore Hi which may be of any magnetic or non-magnetic material and thecore form may be of any type. Insulation H is placed on core [El andsingle layer primary winding I2 of Np turns is wound thereon. Insulationi3 is placed on winding I2 and single layer auxiliary winding l6 of Naturns is wound thereon. Additional insulation of thickness equal to 13is placed on auxiliary winding l6 and single layer secondary windin llof N5 turns is wound thereon, over which is placed insulation 18. Theauxiliary winding I6 is thus located half way between windings I 2 and Il. The left ends of the. windings are at ground potential.

When a voltage is applied to primary winding 12 there are induced inauxiliary winding l5 and. secondary winding l1 voltages dependent uponthe voltage of winding 12 and the ratio of turns between winding l2 andthe respective windings.

If the number of turns of winding I6 is equal to (NS+N,,), the voltageinduced in winding IE will be the average Of that in winding l2 and thatinduced in winding [1. Furthermore, each turn of winding it will thenhave a potential equal to the average of that in the nearest primary andsecondary turns. These potentials are the same as would existtheoretically at the location of the auxiliary winding turns in anabsolutely uniform dielectric without any auxiliary winding. Sincedielectric materials in practice are not uniform, the potentials atthese points would ordinarily depart from the ideal values, resulting inexcessive gradients in portions of the insulation. Thus the auxiliarywinding by maintaining the mid-section of the insulation at the properpotentials provides more nearly uniform potential gradients throughoutthe insulation. This increases the effectiveness of the insulation andpermits a substantial reduction in its thickness without decreasing thesafety factor.

More than one auxiliary winding may be used if desired. If two auxiliarywindings are used and are spaced at equal intervals between the primarywinding having Np turns and the secondary winding having NS turns, thenthe number of turns in that winding which is nearer the primary windingshould be equal to %(2N +N=) .with one and the number of turns in theauxiliary winding nearer the secondary winding should be equal to /3(N-l-2Ns). In this way the potential gradient will be maintainedsubstantially uniform throughout the insulation.

A transformer having two auxiliary windings is illustrated schematicallyin Fig. 3. In this case the number of turns in auxiliary winding 25 maybe equal to /3(2.Np+1vs) and be spaced from winding l2 one-third thedistance between windings l2 and l'i, while the number of turns inauxiliary winding 2i may be equal to /3(N l-2Ns) and be spaced. fromwinding l2 two-thirds of the distance between windings l2 and ll.

In Fig. 4 there is illustrated the arrangement when an electrostaticshield is used. As is usual in such cases, shield 22 is shown groundedat 23. Since the shield is at ground potential and the primary winding 5is the low potential winding, the potential t between winding :2 and orimportance. Auxiliary shield 22 is not 0. winding is, therelore,positioned with ref r ence to the shield 22 and high voltag wind i? andshould have c e half the number of turns of wi ding i'l if 5 mod fromshield the distance between shield "I: and winding ii.

If two auxiliary windings and a shield are used,

the distance between the shield and the high voltage winding controlsand the auxiliary windings may be spaced at equal intervals between theshield and the high voltage winding. The auxiliary winding nearer theshield should have one-third and the other auxiliary winding twothirdsthe number of turns of the high voltage winding.

Fig. 5 is a schematic of a transformer having an electrostatic shield 22and two an ary windlug 25 and located between primary winding l2 andsecondary winding il Auxiliary winding 25 should have one-third thenumber of turns of secondary winding H and be spaced from shield 22on.ethird the distance between the shield and winding ll while auxiliarywind should have two-thirds the number of turns of winding 9! be spacedfrom shi ld 22 twothirds the distance between the shield and winding ll.

the dra il'lg l of the windings are shown connected. to ground. Thegrounded termi--al for the primary and secondary windings is notessential and may be omitted if desired. However, the connection toground of one terminal of the auxiliary winding or win ings ispreferable to insure that the auxiliary winding does not float.

The inventi may also be applied to configurations other than cylindricalwindings. The turns of the auxiliary winding or windings be embedded inthe insulation of a coil of any structure to fix the potentials atparticular points within the body of the insulation to predeterminedvalues. these means the potential gradients may be controlled so toavoid excessive values.

The present invention is of particular value where the voltage developedacross the secondary winding is of the order or" 10,0520 volts. orhigher.

It is desired to point out also that the potential gradient becontrolled to give any desired values. If for any reason it is desiredthat the potential gradient be other than uniform, the position andnumber of turns of the auxiliary windings may be arranged accordingly.

The invention may be carried out in other specificways than those hereinset forth without one-halt 4 departing from the spirit and essentialcharacteristics of the invention and the present embodiment is,therefore, to be considered in all respects as illustrative and notrestrictive and all changes coming within the meaning and equivalencyrange of the appended claims are to be embraced therein.

What is claimed is: V

1. A high voltage electrical transformer comprising a primary winding, asecondary winding,

insulation separating said windings, and means for insuring asubstantially uniform potential gradient between said windings, saidmeans comprising an open circuited auxiliary winding placed between saidprimary and secondary windings and insulated therefrom, the number ofturns in said auxiliary winding being such as to cause to be induced ineach elementary portion of said auxiliary winding a potential which issubstantially the same as would exist at the relative location of saidportion in an absolutely uniform dielectric in the absence of saidauxiliary winding.

2. A high voltage electrical transformer comprising a primary winding, asecondary winding, insulation separating said windings, and means forinsuring a substantially uniform potential gradient in said insulation,said means comprising an open circuited auxiliary winding locatedbetween said primary and secondary windings, the relation of the numberof turns in said auxiliary winding to the number of turns insaid otherwindings determining the distance between said auxiliary winding andsaid other windings.

3. A high voltage electrical transformer comprising a primary winding, asecondary Winding adapted to have developed across its terminals analternating current voltage at least of the order of 10,000 volts,insulation separating said windings, and an open-circuited auxiliarywinding located substantially half way between said primary andsecondary windings, the number of turns in said auxiliary winding beingsubstantially equal to one-half the sum of the number of turns in saidprimary and secondary windings.

4. A high voltage electrical transformer comprising a primary winding, asecondary winding, insulation separating said windings, and a pluralityof open-circuited auxiliary windings between said primary and secondarywindings, said auxiliary windings having different numbers of turns, theauxiliary winding having the larger number of turns being positionednearer said secondary winding.

5. A high voltage electrical transformer comprising a primary winding, asecondary winding, a grounded electrostatic shield therebetween, anopen-circuited auxiliary winding and insulation separating said shieldand windings, said auxiliary winding having about one-half the number ofturns of said secondary winding and being positioned about half-waybetween said shield and said secondary winding.

6; A high voltage electrical transformer comprising a primary winding, asecondary winding, insulation separating said windings, and a pluralityof open circuited auxiliary windings between said primary and secondarywindings, the number of turns of said auxiliary windings and theirlocation in reference to said primary and secondary windings beingdetermined by the potentials which would exist in an absolutely uniformdielectric at the positions of said auxiliary windings.

'7. A high voltage electrical transformer com- 5 prising a single layerprimary winding, a single layer secondary winding surrounding saidprimary winding and spaced therefrom, insulation between said windings,and means for insuring a substantially uniform potential gradientbetween said windings, said means comprising an open-circuited singlelayer auxiliary winding spaced between said primary and said secondarywindings and insulated therefrom, one end of said 6 auxiliary windingbeing substantially at ground potential, the number of turns in saidauxiliary winding being such as to cause to be induced in an elementaryportion of said auxiliary winding a potential which is substantially thesame as would exist at the relative location of said portion in anabsolutely uniform dielectric in the absence of said auxiliary winding.

ALBERT G. GANZ.

